1. Field of the Invention
This invention relates to a heat exchanger for use as a condenser or evaporator for an air conditioner, a radiator or a heater core for a motor vehicle or to other types of heat exchangers, and more particularly, to the fabrication or manufacture of the manifold or header of the heat exchanger.
2. Description of the Prior Art
Heat exchangers generally include two cylindrical headers or manifolds which introduce a cooling medium into tubes and discharge it after it has circulated through the tubes. Heat exchangers of this type are used in automotive vehicles for several purposes, such as a radiator for cooling the engine and as a condenser for an air-conditioning coolant. The manifolds have often been formed each from a length of prefabricated pipe or from an extrusion and thereafter finished to incorporate a plurality of spaced slots along one side for connection to the cooling tubes. These manifolds also have end caps on each end and connections for the introduction of the cooling medium. After assembly of the heat exchanger components, the assembly is usually brazed in an oven to join the elements together as assembled and provide a sealed vessel for the cooling medium.
Instead of forming the manifolds from prefabricated pipe or from a tubular extrusion, several alternative designs have also been proposed for forming the manifolds by forming a flat plate or sheet material into a tube and attaching the side edges together to achieve a tubular shape. One problem of this approach is that the side edge connection is often unreliable and unable to withstand the pressures experienced during operation of the heat exchanger. The side edge connection is particularly prone to burst under pressures at or slightly above normal operating pressures when the heat exchanger is used as a condenser.
Several schemes have been proposed to improve this connection in order to improve the burst strength of the manifold.
U.S. Pat. No. 4,945,635 issued to Nobusue et al. forms the manifold from a brazing sheet rolled into a tube and connected along its longitudinal edge by the brazing operation. Such a connection lacks the inherent strength needed in many heat exchanger applications.
U.S. Pat. No. 5,172,762, issued to Shimura et al. forms the manifold header by bending a longitudinal flat plate into a pipe shape and connecting the side edge portions together with a longitudinally extending groove and raised tab. This side edge connection requires that the side edges be distorted radially in order for the groove to fit over the tab, complicating the fabrication of the manifold.
U.S. Pat. No. 5,214,847, issued to Aoki, also forms the header from a plate, and connects the side edges of the plate together by providing the seam between the side edges where the cooling tubes join the header, and by engaging the tubes and using the engagement to provide a fiction fit. While this arrangement provides a stronger connection than the previously discussed arrangements, the friction fit still has limited strength when the heat exchanger is used as a condenser and the heat exchanger is exposed to higher pressures.
U.S. Pat. No. 5,649,588, issued to Lee, provides a condenser which has a manifolds or headers formed of a flat sheet of metal formed into a tube. The side edges are formed into flanges which are welded together, and the flanges also provide the mounting bracket for the condenser. The welding involves an additional step in the formation of the header or manifold which adds to its expense.
Another prior art design forms the manifold header from a sheet or plate and connects the side edges together with an interlocking design that involves tongues on one side edge which fit into corresponding recesses on the other side edge. The tongues are of the design similar to those used in jigsaw puzzles, so that radial movement of one of the side edges is required to interlock the side edges. This radial movement is difficult to achieve in many forming operations, which adds to the complexity and expense of the fabrication of the header.